The invention relates to a zirconium based material and more particularly to methods for improved corrosion resistance of Zircaloy-4 strip material (as opposed to other alloys or to Zircaloy-4 tubing).
In the development of nuclear reactors, such as pressurized water reactors and boiling water reactors, fuel designs impose significantly increased demands on all of the core strip and tubular cladding (strip is used for grids, guide tubes, and the like). The corrosion of strip is somewhat different from that of cladding as the two have quite different texture (strip is rolled, while cladding is pilgered). Such components are conventionally fabricated from the zirconium-based alloys, Zircaloy-2 and Zircaloy-4. Increased demands on such components will be in the form of longer required residence times and thinner structural members, both of which cause potential corrosion and/or hydriding problems.
Commercial reactors generally use either Zircaloy-2 or Zircaloy-4, (see U.S. Pat. Nos. 2,772,964 and 3,148,055). Zircaloy-2 is a zirconium alloy having about 1.2-1.7 weight percent (all percents herein are weight percent) tin, 0.07-0.20 percent iron, about 0.05-0.15 percent chromium, and about 0.03-0.08 percent nickel. Zircaloy-4 contains about 1.2-1.7 percent tin, about 0.18-0.24 percent iron, and about 0.07-0.13 percent chromium.
Fabrication schedules for Zircaloy-4 have been developed with regard to corrosion resistance. Generally, different processing methods result in either good uniform or good nodular corrosion resistance but not both. The effect of thermal treatment variations has been accounted for by the cumulative A-parameter (see Steinberg, et al. "Zirconium in the Nuclear Industry: Sixth International Symposium, ASTM STP 824, American Society for Testing and Materials, Philadelphia, 1984). Charquet, et al. (see D. Charquet, et al. "Influence of Variations in Early Fabrication Steps on Corrosion, Mechanical Properties and Structures of Zircaloy-4 Products", Zirconium in the Nuclear Industry: Seventh International Symposium, ASTM, STP 939, ASTM, 1987, pp. 431-447) investigated the effects of early stage tube processing on uniform (400.degree. C.) and nodular (500.degree. C.) corrosion. Charquet's results showed that, with increasing cumulative A-parameter, nodular corrosion increases, but that uniform corrosion decreases.